Vehicles in which a geared transmission and a continuously transmission are arranged parallel to each other between an input shaft to which a power of the prime mover is delivered and an output shaft are known in the conventional art. The geared transmission is adapted to select a fixed gear stage from a plurality of gear stages, and the continuously variable transmission is adapted to change a speed ratio continuously. In the vehicle of this kind, a clutch is arranged to switch a power transmission route between a route including the geared transmission and a route including the continuously variable transmission. It is also known in the art that the geared transmission is adapted to establish a fixed gear stage that cannot be established by the continuously variable transmission. Various kinds of control systems and methods for switching the power transmission route in this kind of vehicles have been proposed.
For example, Japanese Patent Laid-Opens Nos. 03-061762 and 63-101561 describe a control system and a control method for the vehicle in which the geared transmission and a continuously variable transmission are arranged parallel to each other between the input shaft and the output shaft. According to the teachings of Japanese Patent Laid-Open No. 03-061762, a speed change operation of the continuously variable transmission is inhibited until completion of a shifting of the power transmission route from the route including the geared transmission to the route including the continuously variable transmission, so as to maintain a speed ratio on the continuously variable transmission to a maximum ratio from a commencement to a completion of the shifting operation. For this reason, the vehicle is allowed to be propelled utilizing a decelerating effect of the maximum speed ratio when the power transmission route to the route including the continuously variable transmission.
According to the teachings of Japanese Patent Laid-Open No. 63-101561, a speed ratio of the continuously variable transmission is adjusted to a target ratio simultaneously with releasing a lockup clutch to disconnect the input shaft from the geared transmission, when shifting the power transmission route from the route including the geared transmission to the route including the continuously variable transmission. In addition, when shifting the power transmission route, a torque transmitting capacity of a starting clutch that is brought into engagement during propelling the vehicle by delivering power through the route including the continuously variable transmission is reduced with an increase in a difference or a ratio between an input speed and an output speed of the starting clutch.
However, according to the teachings of Japanese Patent Laid-Open No. 03-061762, the continuously variable transmission is allowed to change a speed ratio thereof from a point at which the power transmission route is switched. That is, the speed ratio may be changed stepwise before and after the switching operation of the power transmission route. For this reason, a speed change operation may not be performed smoothly. In addition, it may take time to achieve a target speed ratio calculated based on a vehicle speed. On the other hand, according to the teachings of Japanese Patent Laid-Open No. 63-101561, a torque transmitting capacity of the starting clutch is controlled irrespective of a speed ratio of the continuously variable transmission.